November 21, 2015

Generating kilotesla magnetic fields with petawatt lasers

A group of researchers at the Institute of Laser Engineering of Osaka University, the Graduate School of Engineering of Hiroshima University, the Institute for Laser Technology, the Interdisciplinary Graduate School of Engineering Sciences of Kyushu University, and the National Institute for Fusion Science, succeeded in laboratory generation of a magnetic field of 1.5 kilotesla (about 50 million times that of terrestrial magnetism). They achieved the generation of this strong magnetic field when a capacitor-coil target (invented by Osaka University) was driven by two beams from the high-power neodymium-doped glass laser, the GEKKO XII Laser.

Laboratory generation of strong magnetic fields opens new frontiers in plasma and beam physics, astro- and solar-physics, materials science, and atomic and molecular physics. Although kilotesla magnetic fields have already been produced by magnetic flux compression using an imploding metal tube or plasma shell, accessibility at multiple points and better controlled shapes of the field are desirable. Here we have generated kilotesla magnetic fields using a capacitor-coil target, in which two nickel disks are connected by a U-turn coil. A magnetic flux density of 1.5 kT was measured using the Faraday effect 650 μm away from the coil, when the capacitor was driven by two beams from the GEKKO-XII laser (at 1 kJ (total), 1.3 ns, 0.53 or 1 μm, and 5 × 10^16 W/cm2).

Kilotesla Magnetic Field due to a Capacitor-Coil Target Driven by High Power Laser

Magnetic field is generated spontaneously in a laser-produced plasma, and several kilotesla field has been measured in a relativistically intense laser-plasma interaction experiment in small spatial and temporal scales. Kilotesla fields have been produced by magnetic flux compression using imploding metal tubes and plasma shells. Up to 4 kT has been generated by compressing a 6-T seed magnetic field at the OMEGA laser facility.

Fast ignition has high potential to ignite a fusion fuel with only about one tenth of laser energy necessary for the central ignition. One of the most advanced fast ignition programs is the Fast Ignition Realization Experiment (FIREX). The goal of itsfirst phase is to demonstrate ignition temperature of 5 keV, followed by the second phase to demonstrate ignition-and-burn. As for the heating laser, a high-energy peta-Watt laser called LFEX (Laser for Fusion EXperiment) was fully commissioned in the end of 2014. It consists of a 4-beam and 4-path Nd:glass amplifier system with a 40-cm square aperture in each beam. The design goal of LFEX is to deliver 10-kJ energy in 10-ps width at 1-µm wavelength.

In July, 2015, the team at the university's Institute of Laser Engineering emitted a 2-petawatt, or 2 quadrillion-watt, laser beam using the huge "LFEX" (Laser for Fast Ignition Experiments).

The LFEX is about 100 meters long, including the observation apparatus. The four set of devices to amplify the laser beam were completed at the end of last year.

Ultrapower Lasers are improving by 1000 times every ten years.

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